1. Field of the Invention
This invention relates to a communication system and, more particularly, to a synchronous communication system formed as a ring network of two or more ports coupled to one another. The ports are preferably associated with a single multimedia device, and the network is formed between ports of the device to which the external multimedia device is coupled.
2. Description of Relevant Art
A communication system is generally known as a system that permits communication between nodes interconnected by a transmission line. Each node can transmit information, and/or can receive information, across the transmission line. The communication system of interconnected nodes can be organized in various topologies, such as bus, ring, star, or tree topology.
A bus topology network is generally regarded as linear, where transmissions from one node propagate the length of the transmission line and are received by all other nodes connected to that bus. A ring topology network, however, generally consists of a series of nodes connected to one another by unidirectional transmission links to form a single, closed loop. Examples of a ring network are described in IEEE 802.5 and Fiber Distributed Data Interface (FDDI).
Streaming data as used to transfer audio and video data has a temporal relationship between samples produced from a source port onto the network. The relationship between those samples must be maintained across the transmission line to prevent perceptible errors, such as gaps or altered frequencies. A loss in the temporal relationship can cause a receiver at a destination to experience jitter, echo, or in the worst instance, periodic blanks in the audio and video stream. A network that forwards streaming data is preferably synchronous, with each source and destination node sampling at a rate synchronous to the network.
While streaming data is typically sent synchronously across a network, there may be instances in which the sample rate local to a node is not at the same frequency as the frame synchronization rate of the transmission line. If this is the case, then the data streaming from a source device can be sample rate converted, and then sent synchronously across the network. Alternatively, the data can be sent isochronously across the network. There are different types of isochronous data streams. First, the sampling rate may not be synchronized to the network frame rate. Here the number of bytes per frame may vary slightly from frame to frame. An example of this is a 44.1 kHz audio stream transported by a 48 kHz frame rate. A second type of isochronous data streams may be a bursty signal with varying data volumes at constant time intervals. Such signal may be MPEG transport streams. In a third type of isochronous data, there may be varying data volumes at varying time intervals.
To connect a plurality of network nodes to a ring network, a hub as disclosed in US Publication No. 2005/0271068 may be used. However, a problem with the disclosed hub is that it does not reduce the network load as it only forwards the received data. A router is required to decrease network load and increase network throughput.
A router for Ethernet is disclosed in US Publication No. 2008/0002732. The drawback of such a router is that it requires increasing amounts of buffer memory and processing power with increasing network connections and data throughput. Due to buffering, a synchronous real-time transmission of data is not possible.
For transferring streaming multimedia data, like audio and video data, over non-deterministic networks like Ethernet, QoS (Quality of Service) mechanisms are implemented. These require further processing capabilities and excessive memory for buffering of lower priority frames. This can hardly be integrated into a microcontroller.